[numeric-input] NumericInput label cleanup
[numeric-input] NumericInput label cleanup

Summary:
Moving labels outside of `NumberInput`s because I intend
to remove the `label` prop from `NumberInput`.

Test Plan:
Made a numeric-input and edited the `Max error` field,
and tried grading with an answer that fell inside the
error range.

Reviewers: alex

Reviewed By: alex

Differential Revision: https://phabricator.khanacademy.org/D16309

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